I've worked either as staff or contractor for a variety of public and private companies, including a few governments where travel expenses are subject to freedom of information requests. I've probably worked under every possible permutation and I haven't found a perfect one yet.

Long ago I resigned myself to losing a little money whether through expenses that can't really be receipted, currency fluctuations, interest charges, etc. These modest amounts are the price I gladly pay not to deal with pettifogging accountants who believe every expense report is an attempt at grand theft larceny.

In the OP's situation I would ask for an advance on expenses and an increase in my credit card limit to avoid having to bill cc interest which I've found an exercise in frustration. It can be tough to determine the exact amount when there are other charges on the bill and with a slow payer the interest keeps accumulating. What you eventually get will probably not cover the entire interest charge.

Currently I run a sole-proprietor consulting business with substantial travel. I have my own corporate card and enough liquidity to pay off the bill when it arrives. That's as close to perfect as I can get. No interest charges and I get all the points.